How concerned should you be about microplastics?

Let’s start with a fact: you don’t, despite what you’ve heard, eat microplastics for a credit card every week. At least not during a normal human diet. But this popular claim has raised alarm, especially as it has been followed by a series of studies that have found microplastics accumulating everywhere – even on the highest mountains, in the deepest ocean trenches and in the most remote polar regions – as well as in human heart tissue, liver, kidneys, breast milk and the bloodstream. If they’re all over the place, and we can show in some scientific studies that they can cause some kind of harm, that’s cause for great concern, right? Well, no, not necessarily.

The reason microplastics are effective everywhere is that plastic really is a wonder. The advent of the first plastic, Bakelite, in the early 20th century ushered in an era of materials produced on demand rather than being harvested from nature. As plastics became thinner and cheaper, they spread far and wide, revolutionizing food packaging, electronics, and medical devices, to name just a few. But their durability has a downside. Tiny particles have been flowing into the environment for more than a century, and they last a long time, which is why they’ve been found in the body tissues and bloodstreams of animals up and down the food chain – including us – and in many things we consume, such as salt, beer and drinking water.

So yes, microplastics are probably in you. But don’t worry just yet. When we think about any kind of pollution in the body, we have to consider several things. First, there is the question of size, and for microplastics there is a wide range. Then there is what dosage will show any effect. And finally, whether that effect is actually harmful. Since many of the studies involve animals, we must also ask whether these animal studies can reasonably apply to the average human.

The credit card requirement

For microplastics, many of the most worrying headlines in the news in recent years have been vague about the size of the microplastics in question, or they have been based on studies that use strangely large doses that are unlikely to reflect everyday reality.

The big claim that went viral, and has apparently stuck, was that on average, every person on the planet consumes as much as 5 grams of microplastics per week – or the equivalent of a credit card’s worth. That came from a 2019 study that used some really bad math, and it’s simply not true unless you’re taking a very unusual approach to curbing your spending.

The current study was funded by the World Wildlife Fund in collaboration with the University of Newcastle. It was a review that combined the findings from 59 previous studies on microplastics found in food and water. The problem is that some of the studies only measured the number of microplastic particles in a sample and others measured the mass of microplastic. This meant that the researchers had to rely on estimation to compare the two study types. For example, they estimated the mass of microplastic particles found in drinking water using measurements from seawater and particle counts per liter from drinking water. But microplastics in the ocean and our drinking water are not necessarily the same – if the average size of a microplastic particle in the ocean is much larger than in filtered drinking water, the ultimate calculation will be inflated. Later studies looking at the same data found that it was.

So no, we don’t use 5 grams of microplastics every week – it’s probably far, far less. In fact, one study found that most of the world’s population gets just 0.0041 milligrams per week, which is less than a grain of salt. At that rate, it would take you more than 1.2 million weeks, or more than 23,000 years, to plow through plastic for a credit card. If you’re immortal, go ahead and worry.

The same researchers did simulations to predict that each person will accumulate an average of 12.2 milligrams of microplastics in their lifetime, but that only 41 nanograms will actually be absorbed by the body.

New concerns have also been raised in recent weeks over the quality of studies looking at the amount of microplastics in the body. For example, some studies vaporize tissue samples and then analyze the smoke for the presence of microplastics. But when fat evaporates, it can produce similar molecules, creating a false positive.

What does microplastic do in the body?

But all this only applies to the amount of microplastics we use. What they do with us is another question, and one we don’t have quite solid answers to yet. Some evidence points to behavioral changes and inflammation in mice exposed to microplastics. But the highest dose given to these mice was 1 gram per day, which is astronomical for a human body, let alone a mouse. A study in pigs used 1 gram per week and found that microplastic exposure affected the expression of 86 genes and induced oxidative stress in the pancreas, which is caused when there are not enough antioxidants in the body to get rid of unstable molecules that lead to cell damage. But again, the dosage is unrealistic. In fact, in 2022 the World Health Organization warned in a report that most animal studies use concentrations of microplastics that are much higher than people are typically exposed to, or use larger microplastic particles than are likely to be absorbed by the human body. The report also notes that microplastics circulate through our organs differently than they do in rodents, making it difficult to translate findings to humans.

Preliminary human studies exist, and a recent study found that microplastics can accumulate in plaque along with fat, cholesterol and blood cells. In people who had these plastic-infused plaques, the researchers saw a higher incidence of heart attacks and strokes – but we can only say that these were correlated, and not that the microplastics themselves caused these outcomes.

It is complex to understand what microplastics do to our bodies. Yes, they contain chemicals that can interfere with the body’s processes, but when we consider the risks, we cannot assume that 100 percent of these chemicals will leak into our bodies instantly. Research has shown that when we assume, for example, an average amount of leaching into our gut, it results in a negligible increase in chemical concentration in the surrounding tissue. And these chemicals don’t necessarily increase during life, because they can also leak out of the tissues and pass through the stool.

Concerns have been raised that other toxins linked to microplastics can be brought into the body. Or they can interfere with immune responses, or cause cell damage or inflammation. But do they cause these effects more than, say, other types of air pollution, sun exposure, eating too much sugar or catching a cold? We simply do not know.

It is understandable to think that microplastics could possibly be dangerous to our health, and we should find out if they really are. It’s a claim that feeds our doomerism feelings about the pollution going on around us. And just because we don’t use plastic for a credit card every week doesn’t mean the underlying concerns aren’t valid. But the field is still young, and we do not yet have rigorous data on the effects of microplastics in the body. So I would spend my time worrying about other things until we have more solid research on the effects of microplastics.